The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
A conventional internal combustion engine includes a block and a head, also known as an engine block and an engine head. The block of the engine is a casting with appropriate machined surfaces and threaded holes for attaching the head, a coolant pump (e.g., water pump), oil pan, and other units. In an automobile engine in general is equipped with a cooling system, which is designed to radiate the heat produced as a result of burning in the combustion chamber. The cooling system includes a series of channels (i.e, coolant lines) cast into the block and head, surrounding combustion chambers with circulating water or other coolant, and the coolant circulates through the channels in the block and head, respectively. This type of cooling system is referred as a separated cooling system.
In the conventional separated cooling system, a water pump is provided at a coolant circulating line to supply the coolant to the block and the head, and a radiator for radiating the heat of coolant discharged from the head and block is provided. And a main thermostat is disposed between in the coolant circulating line connecting the radiator and the water pump. The main thermostat controls the coolant supplied to the head and block via a water pump only when the temperature of the coolant is within a predetermined temperature range.
Meanwhile, a block thermostat for controlling flow of coolant discharged from the block is disposed in a cylinder-block-side coolant outlet line. The coolant, having passed through the block thermostat, is mixed with the coolant discharged from the head and supplied to the water pump. The cooling system also includes a bypass line connecting the block thermostat and the water pump. When the temperature of coolant discharged from the block is lower than a predetermined temperature, the block thermostat is closed so that coolant discharged from the coolant outlet line of the block is directly supplied to the water pump via the bypass line.
We have discovered that since the coolant discharged through the cylinder-block-side coolant outlet line is mixed with the coolant discharged from the head, engine warm up in a cold start condition is delayed and also large temperature gradient in the discharged coolant causes difficulties in controlling the temperature of coolant supplied to the block.